1. Field of the Invention
This invention relates generally to shaping and treating processes for web type materials of indefinite length and, more specifically, to an improved process and apparatus for producing corrugated paper products by laminating one or more flat paper webs to one or more corrugated paper webs.
2. Description of Prior Art
Processes and equipment for the manufacture of products such as corrugated paper board are well known in the paper industry. In general, these processes involve forming a web of corrugated paper by passing a flat web through corrugating rolls and laminating the corrugated web to the flat web in a machine known as a Single Facer. A second flat web may then be laminated to the opposite face of the corrugated web to form a double faced board in a machine known as a Double Backer or Double Facer. See, for example, Langston U.S. Pat. No. 2,482,627 and McKee U.S. Pat. No. 2,568,349. The double faced web may then be passed through additional processing equipment such as a Slitter/Scorer which slits a web to appropriate dimensions and applies the desired score marks to form fold lines where needed in the event that the corrugated paper board is destined for use as a container or other folded product.
While double faced corrugated paper board is a common product, a number of variations may be desired. These variants may range from single faced corrugated paper to products employing two or more corrugated webs and three or more flat webs to form multiple thickness corrugated boards.
In addition, it may be desired to produce corrugated paper board having flutes of different sizes or multiply corrugated paper board where the flutes of one ply are different in size from the flutes of another ply.
In order to provide such varying end product capabilities, it is frequently desirable to have several Single Facer machines or slave units interconnected with the Double Backer machine or master unit. See, for example, Evans U.S. Pat. No. 3,977,929. In such a compound processing line it will be apparent that the productivity of the line depends upon the operating speed of the Double Backer or master unit, and it is therefore desirable to control the components of the apparatus so that the Double Backer or master unit operates continuously, or nearly continuously, at the optimum speed. However, it is customary to provide web material such as paper used for the corrugated medium and liner in roll form. As each roll of web material becomes exhausted, it is necessary to slow down the roll stand containing that roll to permit splicing a fresh roll of web material. It has been customary, in order to permit the overall process to continue to operate, to provide a storage or buffer area known as a bridge between each Single Facer machine and the Double Backer machine. In anticipation of a splicing operation, for example, the Single Facer operating speed can be increased to provide an inventory of partially processed web material in the storage or buffer area. Then, when the Single Facer is slowed down for the splicing operation, the Double Backer can continue to operate by withdrawing web material as required from the storage or buffer area. See, for example, Schmidt, et al U.S. Pat. No. 3,970,489. Web speed measurements may be made by means of electrical or mechanical tachometers, see, e.g. Schmidt, et al U.S. Pat. No. 3,970,489 and Stewart, et al U.S. Pat. No. 3,104,997. It is also known to provide means for monitoring the quantity of material on the bridge by measuring the rate at which material is delivered to and withdrawn from the bridge, see Ferara U.S. Pat. No. 3,966,518.
Due to the many operating variables encountered in the overall process, it will be appreciated that each drive unit in the process must be capable of operating at a range of speeds between zero and a maximum and that the optimum speed may be affected by several different factors. Moreover, it is important that when speed changes are required the change should be accomplished smoothly but rapidly so that excessive forces are not generated which may shorten the life of the mechanical equipment or cause undue stress in the web material. At the same time, the changes should be accomplished in as short a time as possible to permit the system quickly to return to a normal mode.